Yes, the efficiency on low speed is quite low. Besides the power factor, the main reason for low efficiency is the secondary winding is much thinner (higher gauge) wire than than the primary winding so it has very high resistance. That is the only way they can make a dual winding motor with the same diameter as the single speeds. Improving the power factor helps but improving 45% efficiency by 20% is still only 54% efficiency and that is not better than a VS at any speed.

A VS can maintain high efficiency down to the lowest speeds because it changes the line frequency and voltage plus it always uses the same winding. One thing to note is the Intelliflo shows a higher efficiency at all speeds while the EcoStar shows a significant decrease in motor efficiency (33%) but that can't really be true because the EcoStar has a much better energy factor at 1000 RPM speed than the Intelliflo. Plus the wire to water efficiency of the EcoStar is 35% (Curve-C) at 1000 RPM which cannot be higher than the motor efficiency so there is clearly an issue with some of the data. Other issues with the data include the Whisperflo where the Whisperflo full rate and up rated version of the same THP pump should be identical and in some cases they are way off. However, from my own observations, most of the data seems to be pretty reasonable but there some glaring errors.